Field of the Disclosure
The present invention is related to power converters. More specifically, examples of the present invention are related to clamping the outputs of power converters.
Background
Switch mode power converters are widely used in power supplies for household or industrial appliances that require a regulated direct current (dc) source for their operation, such as for example battery chargers that are commonly used in electronic mobile devices. Off-line ac-dc converters convert a low frequency (e.g., 50 Hz or 60 Hz) high voltage ac (alternating current) input voltage to a required level of dc output voltage. Various types of switch mode power converters are popular because of their well-regulated output, high efficiency, and small size along with their safety and protection features. Popular topologies of switch mode power converters include flyback, forward, boost, buck, half bridge and full bridge, among many others including resonant types.
Under fault or transient load conditions, the output voltage of power converters can overshoot, potentially damaging the loads to which they are connected. In other configurations, if the regulation voltage is deliberately changed, which might occur for example if the regulated value of the output voltage is changed according to varying voltage requirements of different loads that may be connected to the output of the power converter, a sudden disconnection of the load can leave a high voltage remaining on the power converter output capacitor. The high voltage remaining on the output capacitor of the power converter could then damage a new load that is connected that is not designed to withstand the raised output voltage.
Techniques to clamp these output overvoltage conditions are typically imprecise, such as for example techniques that utilize Zener diodes, or consume excessive power because even slight variations in output voltage outside a regulated threshold value could lead to excessive clamp currents being drawn from the output of the power converter.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.